This invention relates to an electrostatographic machine, but more particularly to such a machine having a novel transfer roller.
In the practice of xerography as described in U.S. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the xerographic plate is electrostatically charged uniformly over its surface and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the original light pattern.
The latent electrostatic image may then be developed by contacting it with a finely divided electrostatically attractable material, such as a resinous powder. The powder is held in the image areas by the electrostatic fields on the layer. Where the field is the greatest, the greatest amount of material is deposited; and where the field is the least, little or no material is deposited. Thus, a powder image is produced in conformity with the light image of the copy being reproduced. The powder image is subsequently transferred to a sheet of paper or other surface and suitably affixed thereto to form a permanent print. The powder image may be affixed by passing the sheet of paper or other surface having the transferred image between a heated roller and a second roller in pressure contact therewith, whereby the powder image becomes fused to the sheet of paper.
The powder image is sometimes transferred to an image receiving member by passing the member between the photoconductive surface including the developed image and a biased transfer roller in contact therewith. One of the problems sometimes encountered in using a biased transfer roller is that the paper tends to wrap itself around the roller during the transfer step or operation. Thus, what is needed is a transfer roller which will eliminate or minimize this paper wrapping problem.